'Boardwalk Empire': Season 4 premiere ratings tackled by NFL game

"Boardwalk Empire" is learning that there are tougher opponents than New Jersey mobsters. Like, say, NFL games.

HBO's Prohibition-era drama returned for Season 4 on Sunday night with 2.4 million total viewers at 9 p.m., according to Nielsen. That was a 17% slide compared with the Season 3 opener a year ago.

A big part of the problem? "Empire" was competing head-to-head against the kickoff of NBC's "Sunday Night Football" franchise, with two perennial top draws, the New York Giants and the Dallas Cowboys. Final ratings for football won't be available until Tuesday, but NBC said that based on ratings in the top TV markets, the game was the fifth-best-rated Sunday game in the regular season.

However, HBO pointed out that the "Empire" numbers were still in line with last season's average (2.3 million). When an 11 p.m. encore was included, "Empire" did 3.2 million for the night.

What did you think of "Empire's" season premiere?